Currently and no doubt in the future, considerable effort is being put into converting existing cellular mobile networks and designing future cellular mobile networks for high-capacity data transmission. Such data transmissions are required, for example, not only to service mobile terminals (for example to allow Internet access for laptop and PDA users) but also to provide broadband Internet access over a wireless local loop. As such, the data rates in such networks are considerably higher than had previously been required simply to transmit voice data.
Accordingly, maximised utilisation of base stations and spectrum in terms of data throughput in the network from the base stations to the terminals is an important goal in any new network design.
One approach which has been proposed by QUALCOMM (a registered trademark, hereinafter RTM) is so-called high data rate (HDR) technology. This technology takes advantage of the bursty nature of data transmissions by allocating each class of user (registered with a particular base station) a fractional time on any one channel. Within predetermined latency constraints (i.e. predetermined maximum times to transmit a predetermined number of bits to a terminal) the fractional time of a channel may be varied to dynamically alter the average data throughput to a particular terminal. This allows the network to provide high data rates for a terminal which instantaneously require high data rates and to reallocate that high data rate to another terminal when it is no longer required by the first terminal.
Although this approach is effective to at least some extent, one significant disadvantage of this technique is that network throughput is compromised by any terminal which is unable to receive data at high coding rates (for example because it has a poor carrier to noise ratio due to its distance from the base station and/or due to poor propagation characteristics in the radio channel between the base station and terminal). Thus if the terminal having a poor carrier to signal ratio requires a relatively large volume of data, a significant portion of the fractional time of a channel will be allocated to that terminal which will degrade the performance of other terminals.